Recently, conjugated diene-based polymers having low running resistance, and excellent abrasion resistance and wet traction are required as rubber materials for tires. In order to decrease the running resistance of tires, the hysteresis loss of a vulcanized rubber is required to decrease. As such rubber materials having low hysteresis loss, natural rubbers are known, but these materials have defects of low wet traction. Recently, a conjugated diene-based polymer such as a styrene-butadiene rubber (hereinafter, will be referred to as SBR) and a butadiene rubber (hereinafter, will be referred to as BR) prepared by an emulsion polymerization or a solution polymerization is used as rubbers for tires.
Meanwhile, a solution polymerization SBR is prepared using an anion polymerization initiator, and in this case, an alkyl lithium is mainly used as the anion polymerization initiator.
However, with regard to the above-described rubbers for tires, the improvement of hysteresis loss or abrasion resistance is insufficient, improving effects by mixing are small, and processability is rather decreased.
Accordingly, development of a polymerization initiator having sufficient improvement of abrasion resistance and excellent processability, and a rubber having excellent exothermic properties together with excellent physical properties such as tensile strength, abrasion resistance and wet traction when mixed silica by using the same, is required.